Various metal oxides, such as titanium dioxide, have emerged as attractive materials for nanostructured thin films. These films may be used, for example, as anodes in lithium ion batteries in electric vehicles and hybrid electric vehicles due to their advantages of minimal volume expansion upon lithium intercalation and an operating voltage that allows for superior safety and superior performance over conventional anodes. Some of these oxides, however, have shortcomings that include poor electrical conductivity as a result of the semiconductor nature of the material and low mobility of metal ions in the crystal structure, both of which lead to a poor rate capability. Theoretical bulk capacity is also limited in conventional anodes.
The poor electrical conductivity has often been addressed through the addition of carbon based conductive additives and/or graphene, while other shortcomings have been addressed by nanostructuring the electrode in the form of nanoparticles, nanorods, nanotubes, nanosheets and nanodisks. This provides for a reduced path for metal ion diffusion and a higher surface area at the electrolyte/electrode interface, which provides surface storage of the metal ions. The utilization of the advantages of nanostructuring, however, are very limited in current systems due to the conventional electrode fabrication process.
Conventional processes include a two-step process involving the synthesis of active material followed by doctor blading the active material along with an additive and an electrically insulating binding agent onto a current collector. This limits the ability to make electrodes with oriented structures and leads to aggregation of the nanostructures during electrode preparation or cycling. Further, the presence of the non-active binder and conducting additive decreases the specific capacity of the battery.
There remains a need, therefore, to resolve the drawbacks associated with current techniques while achieving benefits that allow for the highest specific capacity for the active materials in, for example, an electrode.